The present invention relates to xe2x80x9cactive implantable medical devicesxe2x80x9d as such devices are defined by the Jun. 20, 1990 directive 90/385/CEE of the Council of the European Communities, and more particularly the family of the devices which are able to deliver to the heart pulses of high energy (i.e., energy levels significantly exceeding the energy provided for simple stimulation) to try to terminate a tachyarhythmia. These devices are called xe2x80x9cimplantable defibrillatorsxe2x80x9d or xe2x80x9cimplantable cardiovertorsxe2x80x9d, it being understood, however, that the invention also covers the so-called implantable defibrillator/cardiovertor/pacemakers, and defibrillator/pacemakers.
The known implantable devices typically have two components, namely a pulse generator, and a lead or a system of leads. The pulse generator is responsible for monitoring the cardiac activity and generating pulses of high energy when the heart presents a ventricular arrhythmia that is deemed likely to be susceptible to treatment. When this high energy lies in a range between approximately 0.1 and 10.0 Joules (J), one calls this therapy by the name of xe2x80x9ccardioversionxe2x80x9d and the electric energy delivered is called a xe2x80x9ccardioversion shockxe2x80x9d. When the high energy is higher than approximately 10 J, the electric energy delivered is then called a xe2x80x9cdefibrillation shockxe2x80x9d.
To this generator are connected one or more leads, fitted with electrodes, whose role is to distribute the shock energy to the heart in a suitable manner. European Patent EP-A-0,773,039 and its corresponding U.S. Pat. No. 5,776,165, both assigned to the assignee hereof, ELA Mxc3xa9dical, Montrouge, France, describe such a generator/lead unit with means for selecting an optimal configuration for the application of the cardioversion or defibrillation shock.
The present invention, as discussed below, relates to the particular situation where the pulse generator is connected to a lead known as a xe2x80x9cmono-bodyxe2x80x9d or xe2x80x9csingle-pathxe2x80x9d lead, which is a single lead carrying thereon the various electrodes that are able to deliver the defibrillation and/or cardioversion shock.
The German Patent Application DE-A-198 00 697 (assigned to Biotronik) describes such a single-path lead, including two ventricular electrodes for sensing a cardiac signal, a ventricular electrode for delivery of a shock, an atrial electrode for sensing a cardiac signal, and an atrial electrode for delivery of a shock. The two atrial electrodes (detection and shock) are electrically connected together, which makes it possible to avoid a supplementary (additional) conductor in the lead (i.e., there are four conductors instead of five) and also to avoid an extra connection terminal in the connector head of the defibrillator.
In reality, however the xe2x80x9catrialxe2x80x9d shock electrode is an electrode that is positioned mainly in the high vena cava, and so it does not allow for a suitable sensing of a cardiac signal. For this reason, it is envisaged that an atrial detection electrode, placed indeed in the atrium, is able to collect (sense) the electric activity available at this location within the myocardium. But the measurement of the atrial activity is obtained between this atrial detection electrode and a ground reference (i.e., a measurement in a monopolar mode). This leads to a notable degradation of the signal-to-noise ratio, because the lead is a floating lead.
It is, therefore, an object of the present invention to cure this noted disadvantage by proposing a structure of an improved lead which, without increasing the number of conductors or electric terminals at the generator, gives a better quality measurement of the electric activity in the atrium.
To this end, the lead of the present invention is directed to a lead body carrying a first atrial electrode and a second atrial electrode for sensing an atrial cardiac signal, a first ventricular electrode and a second ventricular electrode for sensing a ventricular cardiac signal, one of these ventricular electrodes also being an electrode for the application of defibrillation or cardioversion shock energy, and a supra-ventricular electrode for the application of the aforementioned defibrillation or cardioversion shock energy. An electric connection, preferably internal to said lead, joins together one of the atrial electrodes and the supra-ventricular electrode, the aforementioned atrial cardiac signal thus being collected by the lead between, on the one hand, the ensemble comprising the supra-ventricular electrode and the atrial electrode connected together, and on the other hand, the other atrial electrode.
In a preferred embodiment, the atrial electrode connected to the supra-ventricular electrode is a proximal electrode, and the other atrial electrode is a distal electrode.